1. Field of the Invention
The present invention relates to a driving method and a driving device for a matrix display-type plasma display panel (hereinafter referred to as PDP)
2. Description of Related Art
AC (alternating current discharge) type PDP is well known as one such matrix display-type display panel.
The AC-type PDP comprises a plurality of column electrodes, and a plurality of row electrodes, which are arranged orthogonal to these column electrodes, and which form one scanning line per pair of electrodes. These respective row electrodes and column electrodes are covered with a dielectric layer for the discharge space, and assume a structure, wherein a discharge cell, which supports a pixel, is formed at each intersecting portion of a pair of row electrodes and a column electrode.
Here, a subfield method is known as one method for implementing an intermediate brightness display for this PDP. In a subfield method, the display period of one field is displayed by being divided into N subfields, which emit light only for a time corresponding to the weighting of each bit digit of N-bits of pixel data.
When using the subfield method, if it is supposed, for example, that the pixel data being supplied is constituted by six bits, a period of one field is divided into six subfields SF1, SF2 . . . , SF6, and emission driving is performed for each subfield.
Each subfield is constituted by a simultaneous resetting step, a pixel data writing step, and an emission sustaining step. In a simultaneous resetting step, by simultaneously causing discharge excitation (reset discharging) of all the discharge cells of the above-mentioned PDP, the wall charges of all the discharge cells are uniformly erased. In the subsequent pixel data writing step, a selective write discharge corresponding to pixel data occurs in each discharge cell. In this state, a wall charge is formed inside a discharge cell in which a write discharge occurred, and this discharge cell is set to an xe2x80x9clight-emitting cell.xe2x80x9d Conversely, since a wall charge is not formed in a discharge cell in which a write discharge did not occur, this cell becomes a xe2x80x9cnon-light-emitting cell.xe2x80x9d In an emission sustaining step, only a discharge cell, which has been set to an xe2x80x9clight-emitting cellxe2x80x9d, is discharged repeatedly during a period of time corresponding to the weighting of each subfield. In this process, a brightness corresponding to the total discharge period implemented in the emission sustaining steps of subfields SF1 through SF6, respectively, is visible. That is, if discharge periods of ratios of 1:2:4:8:16:32 are allocated to each subfield SF1 through SF6, then an intermediate brightness of 64 grayscale levels can be represented.
However, the reset discharge, which was implemented for all discharge cells in this simultaneous resetting step, is accompanied by a relatively strong discharge, that is, an emission of light that is a high level of brightness. The problem is that, since an emission that has nothing in the least to do with pixel data is generated by the reset discharge at this time, this causes a drop in dark contrast when enjoying a darker image, especially inside a darkened room.
Furthermore, in another example, when the pixel data for each pixel based on an input picture signal, for example, is eight bits, a one field display period is divided into eight subfields, and a simultaneous resetting step, a pixel data writing step, and an emission sustaining step are executed sequentially inside each subfield.
In a simultaneous resetting step, discharge excitation (reset discharging) is caused in all the discharge cells of the above-mentioned PDP simultaneously, thereby causing wall charges to be formed inside all the discharge cells. In a pixel data writing step, a discharge occurs selectively (selective erase discharge) for each discharge cell according to the logic level of the pixel data bit corresponding to the subfield thereof. In this process, the wall charge inside a discharge cell in which a selective erase discharge occurred is erased, and this discharge cell is set to a non-light-emitting cell state. Conversely, since the wall charge inside a discharge cell in which a selective erase discharge did not occur remains unchanged, this discharge cell is set to an light-emitting cell state. In an emission sustaining step, only a discharge cell, which has been set to the above-mentioned light-emitting cell state, is repeatedly discharged (sustain discharged) during a period of time corresponding to the weighting of each subfield. In this time, a brightness corresponding to the total number of sustain discharges, which occurred in the respective emission sustaining steps of the eight subfields, is visible. In other words, if numbers of sustain discharges having the ratios of 1:2:4:8:16:32:64:128 are allocated to the eight subfields, respectively, by combining the subfields in which sustain discharges occur within a one field display period, an intermediate brightness of 256 (=28) grayscale levels can be represented.
In driving a PDP in this way, a plurality of discharge cells are subjected to repeated sustain discharges in the emission sustaining steps of the respective subfields to achieve a display of intermediate brightness corresponding to input picture signals. Consequently, the problem is that, since current is applied to the respective discharge cells each time this sustain discharge occurs, a lot of power is consumed.
Furthermore, when a picture signal, which represents a high brightness picture, is supplied, the problem is that, since the number of sustain discharges occurring per unit time to realize this high brightness picture display increases, the power consumption increases in accordance with this.
An object of the present invention is to provide a plasma display driving device, which is capable of enhancing contrast.
A driving device of a plasma display panel according to a first aspect of the present invention is a plasma display panel driving device for driving, in accordance with picture signals, a plasma display panel, in which a plurality of discharge cells supporting display pixels are arranged in a matrix, having resetting means for generating a reset step for causing the occurrence of a reset discharge, which initializes each of the above-mentioned discharge cells to one of either an light-emitting cell state or a non-light-emitting cell state, and applies this to each of the above-mentioned discharge cells; pixel data writing means for applying to the respective above-mentioned discharge cells a scanning pulse for causing the occurrence of a selective discharge, which selectively sets the above-mentioned discharge cells to either the above-mentioned non-light-emitting cell state or the above-mentioned emission-cell state in accordance with pixel data corresponding to the above-mentioned picture signals; emission sustaining means for applying to each of the above-mentioned discharge cells a sustaining pulse for causing the occurrence of a sustain discharge, which causes light to be emitted repeatedly only from the above-mentioned discharge cells that are in the above-mentioned light-emitting cell state; a light sensor for detecting the ambient illuminance of the above-mentioned plasma display panel; and reset step waveform adjusting means for adjusting the level change rate at the leading edge portion of the above-mentioned resetting step in accordance with the above-mentioned illuminance.
Furthermore, a driving device of a plasma display panel according to a second aspect of the present invention is a plasma display panel driving device for driving, in accordance with picture signals, a plasma display panel, in which a plurality of discharge cells supporting display pixels are arranged in a matrix, having resetting means for generating a reset step for causing the occurrence of a reset discharge, which initializes each of the above-mentioned discharge cells to one of either an light-emitting cell state or a non-light-emitting cell state, and applies this to each of the above-mentioned discharge cells; pixel data writing means for applying to each of the above-mentioned discharge cells a scanning pulse for causing the occurrence of a selective discharge, which selectively sets the above-mentioned discharge cells to either the above-mentioned non-light-emitting cell state or the above-mentioned emission-cell state in accordance with pixel data corresponding to the above-mentioned picture signals; emission sustaining means for applying to each of the above-mentioned discharge cells a sustaining pulse for causing the occurrence of a sustain discharge, which causes repeated light emissions only in the above-mentioned discharge cells that are in the above-mentioned light-emitting cell state; and a light sensor for detecting the ambient illuminance of the above-mentioned plasma display panel, and the above-mentioned resetting means changes the number of times, which the above-mentioned resetting step is applied to each of the above-mentioned discharge cells in accordance with the above-mentioned illuminance.
Another object of the present invention is to provide a plasma display panel driving method and driving device, which are capable of holding down power consumption.
A driving method of a plasma display panel according to a third aspect of the present invention is a plasma display panel driving method for driving, in accordance with picture signals, a plasma display panel, in which a plurality of discharge cells supporting display pixels are arranged in a matrix, comprising a pixel data writing step for applying to each of the above-mentioned discharge cells a scanning pulse for causing the occurrence of selective discharge, which selectively sets the above-mentioned discharge cells to either the above-mentioned non-emission state or the above-mentioned emission state in accordance with the pixel data of each of the above-mentioned display pixels corresponding to the above-mentioned picture signals; an emission sustaining step for repeatedly applying to each of the above-mentioned discharge cells a sustaining pulse for causing a sustain discharge only in the above-mentioned discharge cells that are in the above-mentioned light-emitting cell state; and an adjusting step for changing the number of the above-mentioned sustaining pulses per unit time applied to each of the above-mentioned discharge cells in the above-mentioned emission sustaining step in accordance with the ambient illuminance of the above-mentioned plasma display panel, and, in addition, for adjusting the pulse width of at the least one of the above-mentioned scanning pulse and the above-mentioned sustaining pulse.
Furthermore, a driving device of a plasma display panel according to a third aspect of the present invention is a plasma display panel driving device for driving, in accordance with picture signals, a plasma display panel, in which a plurality of discharge cells supporting display pixels are arranged in a matrix, having pixel data writing means for applying to each of the above-mentioned discharge cells a scanning pulse for causing the occurrence of a selective discharge, which selectively sets the above-mentioned discharge cells to either the above-mentioned non-light-emitting cell state or the above-mentioned emission-cell state in accordance with the pixel data of each of the above-mentioned display pixels corresponding to the above-mentioned picture signals; emission sustaining means for repeatedly applying to each of the above-mentioned discharge cells a sustaining pulse for causing a sustain discharge only in the above-mentioned discharge cells that are in the above-mentioned light-emitting cell state; an external light sensor for detecting illuminance surrounding the above-mentioned plasma display panel; and adjusting means for changing the number of the above-mentioned sustaining pulses per unit time applied to each of the above-mentioned discharge cells in accordance with the above-mentioned illuminance, and, in addition, for adjusting the pulse width of at the least one of the above-mentioned scanning pulse and the above-mentioned sustaining pulse.
A driving method of a plasma display panel according to a fourth aspect of the present invention is a plasma display panel driving method for carrying out a display corresponding to input picture signals by causing discharge to occur by repeatedly applying displaying pulses to each of the above-mentioned discharge cells of a plasma display panel comprising a plurality of discharge cells supporting display pixels, having an average brightness computing step for computing the average brightness of an image displayed in accordance with the above-mentioned input picture signals; an illuminance detecting step for detecting the ambient illuminance of the above-mentioned plasma display panel; and a driving step for computing the application frequency at which the above-mentioned displaying pulse is to be applied using a conversion function, which has the above-mentioned average brightness and above-mentioned illuminance as parameters, and applying to each of the above-mentioned discharge cells the above-mentioned displaying pulse in accordance with the above-mentioned application frequency.
Furthermore, a driving device of a plasma display panel according to a fourth aspect of the present invention is a plasma display panel driving device for carrying out a display corresponding to input picture signals by causing discharge to occur by repeatedly applying displaying pulses to each of the above-mentioned discharge cells of a plasma display panel comprising a plurality of discharge cells supporting display pixels, having average brightness computing means for computing the average brightness of an image displayed in accordance with the above-mentioned input picture signals; illuminance detecting means for detecting the ambient illuminance of the above-mentioned plasma display panel; and driving means for computing the application frequency at which the above-mentioned displaying pulse is to be applied using a conversion function, which has the above-mentioned average brightness and above-mentioned illuminance as parameters, and applying to each of the above-mentioned discharge cells the above-mentioned displaying pulse in accordance with the above-mentioned application frequency.